Nobody had set any records in their alternate fuel classes, so I prepped my single-speed Yanmar clone for the job. I figured it would be easy, just show up, race, and get a record, but it took me about 6 months to make it legal for the competition.

The bike after I upgraded the electricals with a dead man's switch (the lanyard on the left handlebar) and a proper exhaust system to "direct exhaust away from the racing surface". I used unbaffled straight pipes, and definetely noticed a major power increase.

The layout of the drivetrain after major modifications. I replaced the side panels andc converted them to number boards, made struts to replace the rear shocks and mounted a homemade aluminum chain guard (race requirement). I also added a smaller sprocket to up the top speed to 55ish, made a clutch cover, and added a smaller battery tta could be fastened with a metal strap.

I installed street tires to cut back the rolling resistance. It is fairly difficult to find modern tires with unbroken ribs in the center of the contact surface, but I finally found a type of Metzler that worked. I used the same tire front and back, but almost ran into disaster when the tire started rubbing against the front fender! Apparently, 4.00x18 tires don't have consistent sizes; the previous knobbys were supposedly the same size and they had plenty of clearance. I had to modify some mounting hardware to make it work.

This is more or less the final configuration before I left for Maine

The mighty Ranger and the glorified mini bike at Loring.

The return lane. This abandoned runway is supposedly the 14th longest in the world. The actual race course, 20 yards east, is 13th longest.

After a disappointing first pass (42 mph) we decided to take the axe to everything not required by the rules. goodbye fender, brakes, taillight, and airbox. All this paid off in the next run, when the bike hit 50.09 mph

Lean and mean. My top speed, and the new record, is 56.5 mph in my final pass. I think the engine was running somewhere around 3700 rpm, so I should be able to increase that and improve a little next year

The next class up is partial streamlining, and that allows as much fiberglass as I want, as long as you can see my entire body from the side. I plan on running for the partially streamlined 500cc class next year with this:

junkyard Suzuki GS550E. I think there is another post for it somewhere on this thread, but the project kinda got put on the back burner for a while. Now that the first one is "done", I think I'll start with this. I already have a little EMGO fairing that I might use.

i originally wanted to put on a 5 speed and stretch the frame, but they have pretty strict standards at the track and i want to keep as much of the original loop as possible. I think i can put on a CVT like Dougy's Harley and only have to modify the right downtube.

This is what it looks like in my head, we'll see if I can come close

I haven't decided whether to leave the kawi as is or try to improve it with a CVT for next year, so i think I'll sit on it for a while and figure that out later.

Just a quick status update on the project: I finished the two-speed, and it worked correctly for about 3 days.

Then I discovered that locking sprag bearings fail when they come into contact with grease containing moly, PTFE, or Graphite. Of course it wasn't labeled as containing any of these, but whatever. Long story short, wrecked the bearing, and had to come up with a homemade solution. I made a ratcheting gear on my 100 year old mill:

This worked well, and lasted long enough for me to record a video of the bike running with the new engine mods and exhaust system:

Unfortunately, the shoulderscrew I used to locate the ratchet pawl failed and sheared off about an hour later. In addition, the return spring collapsed, and in an apparently unrelated event, the fuel cutoff solenoid on the pump failed. Only 3.5 months to go!

All the other transmission types require stretching the frame, and I wanted to maintain the original dimensions of the bike so I could reuse all the stock parts. Also, you experience a certain amount of power loss through friction when you use V-belts.

coachgeo wrote:wouldn't this be sort of a wash out have basically infinate ratios between two points

Thats true, and that is very useful when you're mostly using the bike on the road with constanty changing conditions. I am trying to optimize it for flat ground, straight line, high speed situations, and the engineer in me likes predictable repeatability I don't have much experience with CVT's, so I wanted to focus on pre-determined gears so i could dial it in more easily.

Note to self, don't use sintered steel sprockets in the future. Apparently they can't handle shock loads. The pawl punched a chunk of the ratchet sprocket right out during a test ride today. I'll remachine it from carbon steel this weekend.

On the plus side, the stronger pawl hinge bolt that I made was the only part of the assembly to survive

Congratulations! Nicely done. Nice movie as well. However it seemed to me that however you tuned the engine up to 4500 RPM it didn't go near there. I have the feeling that if you would use a larger rear sprocket, it might just have some extra power to overcome wind resistance an maybe gain some extra speed. But, nevertheless, you did it again .

You got that exactly right. This video was one of the first runs before I got everything sorted. The gearing was all wrong, and I was stuck at 4000 rpm, plus I was dealing with some nasty head/crosswinds. On day three I got everything figured out and meshing correctly, and that's when I made all the record passes. I'll try to post a few more updates that go into more detail over the next week.

I finally have a chance to sit down and cover the last few months of updates. After blowing the second sprag sprocket design, I made a new one using a sprocket made of hardened tool steel, with a pressed-on ring to reinforce it.

This design still had a major flaw. The ratchet pawl had a habit of flattening out and mushrooming at the tip, which would prevent it from seating and cause it to break and lock the ratchet. I solved that by filing large chamfers on the sides of the contact edge, and oil hardening the parts, but this still needed to be rebuilt every 20-30 miles or so. This was good enough for racing, but I wanted to eventually use the bike on the road.

The final design uses four ball bearings that sit in ramps on the inner collar that is locked to the shaft. The sprocket has a series of shallow notches machined into its inner surface, and when it spins in the direction of the ramps, the balls roll into the notches and lock the parts together. So far, this design has lasted for over 100 miles without fault.

The last major change I made was to replace the ANSI Type 40 roller chain with SAE Type 420 O-ring chain. This is compatible with ANSI 41 sprockets, so I remachined the sprockets to the correct width. The regular chain was throwing off the grease too quickly and then seizing links, and O-ring chain will last longer.

I've also completed a full set of blueprints, the associated documentation, and a full costed out parts-list for this transmission design. If anyone is interested in making a copy of this design, or having parts manufactured by me for their project, you can PM me at John.W.Petsche@gmail.com. Cheers!

Last edited by HondaJohn on Fri Jan 04, 2013 6:08 am, edited 1 time in total.

I once had to analyze some Yanmar clones for a project, and I discovered that the first major design flaw is the valve springs. They are extremely weak which can lead to valve float and sloppy timing at higher rpm's. To get more revs out of the engine, I replaced the valve springs with a stronger set to reduce float. They can be purchased here:

I used part number GP961-2. They are a mild performance upgrade for briggs and stratton flathead engines. They are nearly the same dimensions as the original springs in the L70 clones, and can be substituted with no other modification. Although slightly wider in diameter, it is not enough to cause them to shift out of place. I've put nearly 300 miles on my engine with these installed and have not noticed any problems. They allow me to run the engine reliably at 4000 rpm. I cannot guarantee the longevity of the engine at these speeds, but in the short term it gives a decent performance boost

I haven't had a reason to pull apart the head yet so I don't know if there has been an increase in wear. I haven't heard any interesting new sounds coming from the engine though The new springs aren't much stronger anyway. I calculated that the original ones had a seat strength of 17.375 lbs and a cam lobe nose strength of 39.1 lbs. The new springs have a seat strength of 20-25 lbs and a nose strength of 45-50 lbs. Its a relatively small increase in stress. However, next time I get a chance to tear it apart I'll report what I find.